I. Technical Field
The present invention relates to a hydrodynamic bearing which is used in motors and the like for rotationally driving recording discs such as magnetic discs, optical discs and the like, and in particular, to a hydrodynamic bearing which is compatible with miniaturization of motors, a motor including the same, and a recording and reproducing apparatus.
II. Description of the Related Art
Recently, recording apparatuses for rotationally driving recording media having a disc shape, such as magnetic discs, optical discs, magneto-optical discs, and the like have increased memory capacity and a higher transfer rate of data. Thus, bearings used in such recording apparatuses are required to hold a shaft which is driven to rotate at a high speed with high precision. Hydrodynamic bearings are used as bearings which satisfy such requirements.
In order to address the problem of a vibration due to motor imbalance or turbulence of an air flow inside a hard disc drive (hereinafter, referred to as HDD), for example, in an axial direction, forces to support the bearing at two points are enhanced by increasing the pressure peak of a radial bearing portion at two points to increase moment rigidity of the bearing portion. For improving the pressure peak of the radial bearing portion, in general, a bearing span, a groove angle of a hydrodynamic groove, a groove width ratio, a groove depth, or the like is modified.
For example, Japanese Laid-Open Publication No. 62-270816 discloses a hydrodynamic bearing which has a herringbone groove with an angle of 80 degrees or larger and below 90 degrees formed between two sets of helical grooves having an angle (groove angle) of 15 to 45 degrees with respect to the axial direction to allow an increase in the pressure generated at the hydrodynamic groove. Japanese Laid-Open Publication No. 63-266209 discloses a hydrodynamic bearing which includes a groove which connects a set of partial grooves (open V-shaped grooves) to allow improving a pressure generated at a hydrodynamic groove. Japanese Laid-Open Publication No. 7-269560 discloses a hydrodynamic bearing which includes a herringbone groove which is at least partially curved to allow increasing a pressure generated at a hydrodynamic groove. In each of the Japanese Laid-Open Publication Nos. 62-270816, 63-266209, and 7-269560, the moment rigidity of the radial portion is increased by modifying the shape of the hydrodynamic grooves and increasing the pressure generation peak.